This invention relates to video displays and more specifically to a moving map display using a flying spot scanner.
Moving map displays are utilized for navigating vehicles such as aircraft, and displaying a segment of a map with a symbolic image of the vehicle fixed at some point on the face of the display, such as at the center thereof. The display is responsive to signals from on-board navigational equipment for indicating the constantly changing location of the vehicle.
Prior art devices utilize a flying spot scanner to scan a portion of film containing a map which modulates the scanner light beam. The display can be in color or monochromatic. Conventional means such as photodetectors are used to convert the modulated light beam to provide a video signal which is used to display the scanned map portion on a cathode ray tube (CRT) screen. In one prior art scheme the flying spot scanner traces a miniature or "shrunk" raster on a portion of a CRT flying spot scanner tube. This tracing allows the flying spot scanner to scan a small portion of the map on the film, and the displayed map portion is electronically translated and rotated in response to navigational signals. Other arrangements feature various combinations of electronic and electro-mechanical means for accomplishing the translation and rotation. One such arrangement involves the mechanical movement of the map film in one direction and electronically moving the scanner beam of the flying spot scanner in an orthogonal direction. Yet another arrangement involves mechanically moving the map in one direction and the use of a moving mirror in the orthogonal direction.
Electromechanical moving map display techniques are costly, cumbersome, require precise mechanical alignment and are more prone to failures and misalignment than are electronic techniques. Electronically moving a miniature raster generated by a flying spot scanner around the face of the scanner is an improvement over the electromechanical arrangements, but it also suffers a shortcoming: The full resolution capability of the CRT flying spot scanner tube is not achieved, as a very small raster is traced on a correspondingly small portion of its face. There is also a limitation on how close each scan line generated by the scanner can be to another scan line. The end result is a limitation in the amount of "resolution" or detail of the map on film that can be obtained and displayed using this technique.
Another disadvantage exists in that for prior art map readers using map film, the map must be reproduced on the film in such a way that large areas of the reproduced map retains carefully controlled dimensions. This type of map film is necessarily generated by a tedious and therefore costly process as will be understood by those skilled in the art.
In accordance with the above, there is a need in the art for an electronic moving map display, wherein mechanical movement is minimized. There is a further need to more completely utilize the full resolution capability of a flying spot scanner. There is yet a further need to provide a display of the type described wherein the cost of producing map film is minimized while providing the required dimensional accuracy of the map as finally displayed.